This invention relates generally to apparatus for filtering large quantities of transport air having dust or other foreign matter entrained thereon by passing said transport air through a plurality of self-cleaned filter elements, such as filter bags made from an appropriate fabric.
Filters or dust collectors of the foregoing type typically use, as the filtering elements, large bags made from any suitable fabric, such as, for example, 16-ounce polyester felt with nylon scrim reinforcement, or pleated paper filter cartridges. The transport air is passed through the filtering elements, usually from the outside of the bag to the inside, and deposits the entrained dust or foreign matter on the surface of the filtering element, after which the cleaned air is transported away from the dust collector. After a period of time, the length of which depends on many variables, the dust collected on the exterior surface of the filter elements will accumulate to a point at which is must be removed for proper continuing operation of the dust collector, and therefore these dust collectors are provided with some type of arrangement for periodically cleaning the filter elements, usually by the use of a flow of air or air pulse that is transmitted back through the filter elements in a direction opposite to the normal flow of the transport air, whereby the accumulated dust particles are moved outwardly from the surface of the filter element and caused to gradually migrate downwardly until they are removed from the filter element altogether for ultimate removal from the dust collector.
In most of the dust collectors of this type, the filtering elements are mounted on a partition plate to depend downwardly therefrom, and the partition plate is provided with an opening for each filter which permits the cleaned air to flow upwardly through the opening in the partition plate to a clean air chamber located above the partition plate. The apparatus used to clean the filter may take a variety of forms, but it typically includes either a fixed nozzle disposed above and adjacent each opening in the partition plate, or a movable member that is designed to pass over the plurality of partition plate openings and cause the cleaning air to flow through such openings and into the center of the filter.
In typical apparatus of the first type, which is used most often in dust collectors that use cylindrical pleated paper filter elements, a venturi is fixed above the center of each partition plate opening together with a pipe that extends above each venturi with apertures formed in the pipe for periodically emitting a pulse of pressurized air into the venturi which creates a momentary pulse of cleaning air within the filter that passes outwardly therethrough to clean the exterior surface thereof. Typical examples of this type of cleaning apparatus are disclosed in Frey U.S. Pat. No. 4,218,227 and Lissy U.S. Pat. No. 4,409,009.
Where a movable member is used to distribute the cleaning air to the filter, it is usually in the form of a radially extending arm mounted for rotational movement just above the partition plate, and having a plurality of jets or apertures formed therein for directing a flow of air downwardly into the filter through the openings in the partition plate. In most of these dust collectors, the jets or apertures in the moving arm are arranged to correspond in some manner with the pattern of openings in the partition plate, and in some instances cleaning air is discharged from the moving arm in a random manner that is determined by the predetermined pressure buildup across the filter, as disclosed for example in Caplan U.S. Pat. No. 3,487,609, Swanson U.S. Pat. No. 2,974,748 and Smoot U.S. Pat. No. 3,227,633. In another variation, Bosworth U.S. Pat. No. 4,655,799 discloses a dust collector in which the openings in the circular partition plate (and therefore the filters) are arranged in a plurality of contiguous pie shaped segments, each segment having exactly the same pattern of openings therein. The movable arm has jets which are also disposed in exactly the same pattern as the openings in each pie-shaped segment, and a proximity sensor and a counter are utilized together to determine when the jets in the movable arm are directly above a selected one of the pre-shaped segments, whereupon a solenoid is operated to open a valve that connects the jets to a source of pressurized cleaning air and all of the jets exert a blast of air into each of the corresponding openings in the selected pie-shaped segment.
The dust collectors described above which include randomly fired jets of cleaning air are relatively inefficient because there is no way to insure that the jets will be fired when they are centered over a filter, and it is entirely possible that some bags will remain uncleaned for substantial lengths of time, all of which creates higher pressure drops across the filters, increased demands on the total fan system and higher energy costs. In the dust collectors which include cams or other arrangements for firing the cleaning air jets when they are properly positioned above a corresponding pattern of partition plate openings, improved operating efficiency results, but they still have some drawbacks. For example, when the jets in the movable arm are located in a straight line along its radially extending length, the openings in the partition plate must also be arranged in radial lines extending from the center of the partition plate, and this pattern reduces significantly the number of openings, and therefore the number of filters, that can be employed, particularly where the partition plate has a large diameter and the radially outermost openings in each radial line are substantially spaced from one another in an angular direction. While the particular pattern of openings utilized in the aforesaid Bosworth patent overcomes this disadvantage to some extent, there is still a problem of not making maximum utilization of the entire space available for openings on the partition plate. Moreover, in most of the above-described positively fired dust collectors, all of the jets in the movable arm are fired each time the control valve is opened, which can result in inefficiency if all of the filters are being cleaned at the same time intervals even though some of the filters become dirty with different frequencies, such as may be the case, for example, when the radially outermost filters are nearest the dirty air inlet of the dust collector and will therefore tend to accumulate dust more rapidly than the filters which are closer to the center of the partition plate.
By contrast, the filtering apparatus of the present invention overcomes or alleviates the aforesaid drawbacks of known filter apparatus, and provides an electronic control means which can be programmed to selectively vary the sequence and frequency at which the jets of cleaning air are operated.